In the graphics card market, VGA and DVI have quietly retired from the stage of history, Type-C still belongs to the minority, DP and HDMI have become the standard configuration of mainstream graphics cards.
For the vast majority of users, as long as the normal connection and display is not a problem, it does not matter which interface is used at will. But for audio and video enthusiasts, the choice of DP or HDMI is particularly important, especially for high-end displays equipped with HDR, high resolution, high refresh rate (144Hz or higher) and other features. Choosing the wrong interface means that the best performance of the graphics card and monitor can not be achieved.
For the vast majority of users, any interface doesn’t matter as long as the normal connection and display are fine. But for avid gamers, choosing DP or HDMI is especially important, especially for high-end displays equipped with HDR, high resolution, high refresh rate, and other features. Choosing the wrong interface means not achieving the best performance from your graphics card and monitor.
The Development of DP and HDMI
The emergence of DP and HDMI marks the full-scale entry of video transmission interfaces into the digital era. Although the previous DVI interface also used digital signals for transmission, DVI could not transmit audio and data streams. HDMI emerged before DP. the HDMI 1.0 standard was introduced in 2002. The latest standard is now HDMI 2.1, while the DP 1.0 standard was only introduced in 2006. Currently, the latest standard is DP 2.0. Thunderbolt and type-C are technically special forms of DP interfaces, as the digital video signals they transmit are also transmitted via the DP protocol.
After so many years of development, the DP and HDMI interfaces have not changed, but the protocol is evolving and the transmission capacity of different protocol versions is enormous.
DP and HDMI standards are backward compatible, which means that 1.0 transmission lines can still be used under the latest standards, except that there is a barrel effect between the display, transmission lines, and graphics cards, and the display capacity will only be biased towards the lower one.
The most important parameters for each generation of DP and HDMI are the transmission rate and data transfer rate.
Most early DP and HDMI standards use 8b and 10B bit rate encoding for transmission. In actual transmission, 10 bits of transmission bandwidth is required for every 8 bits of data, which means that 80% of the bandwidth can be used for data transmission and additional redundancy is used to ensure signal integrity. Currently DP 2.0 uses both 128B and 132b bit rate encoding for transmission, and the encoding efficiency is increased to 97%. HDMI 2.1 uses 16b and 18B bit rate encoding for transmission, and the encoding efficiency is 88.9%. Therefore, the new generation of DP has a higher data transmission rate than HDMI.
The significance of data transmission bandwidth
Each pixel on a display has three sub-pixels: red, green and blue. Different colors are displayed by adjusting the brightness and chromaticity difference of the sub-pixels. Regardless of the internal operation of the graphics card, the final generated data is converted into a display signal, and this digital video data requires a certain amount of data transmission bandwidth.
Currently, 24-bit color is commonly used, which means that each pixel of red, green, and blue occupies 8 bits of data. In HDR and high color depth displays, the data occupancy of each color is adjusted to 10 bits, and 30-bit color can bring better display effects. Some top professional displays even increase the bit depth to 12 or 16 bits. As the color depth increases, more data needs to be transferred.
As an example.
The bandwidth required to achieve an 8-bit color depth 19201080 @60 Hz display is: 81920108060*3≈2.986Gbps
In fact, the data bandwidth required to achieve 8-bit color depth 1920*1080 @60 Hz is 3.0Gbps. This is because the monitor is using progressive scan to complete the screen switching, and the monitor sets aside some area outside the screen for alignment and clock synchronization during progressive scan.
If the transmission line and interface do not meet the corresponding requirements, the resolution, refresh rate or HDR will be reduced or turned off.
Comparison of the advantages and disadvantages of DP and HDMI
DP 2.0 was released in June 2019, but it still does not support the launch of consumer-grade graphics cards and displays, and the current mainstream is DP 1.4. Currently, 8K displays are mainly TVs, and HDMI 2.1 is used to implement 8K signal transmission. Therefore, in the short term, DP 2.0 products are not promoted on a large scale, and the transmission performance of DP is not as good as that of HDMI 2.1.
However, DP natively supports VRR (Variable Refresh Rate) and to use FreeSync technology (G-Sync compatible), a DP interface must be used. DP can also connect multiple screens to a single port via MST (Multistream Transport) and some displays also support MST for DP connections.
HDMI is a protocol standard that requires certification, while DP is an open protocol standard, so many new technologies (such as DSC, G-Sync, FreeSync, etc.) will appear first on DP and then slowly on HDMI. Variable refresh rate technology will be added to the HDMI 2.1 standard to support FreeSync and G-Sync technologies.
For gamers, the best solution for N cards is a DP connection to the G-Sync feature, as there is currently only one TV with an HDMI 2.1 compatible G-Sync display. Because the A card is relatively loose, the display’s FreeSync feature can be turned on via HDMI.
From a comprehensive point of view, DP is still recommended when connecting to a desktop display. but HDMI has high popularity and compatibility and can be said to be ubiquitous and can be seen in any electronics I. DP transmission cables are limited to 3 meters, while HDMI can reach up to 15 meters. HDMI is perfect for connecting TVs, projectors and other scenarios.
The essential difference between DP and HDMI
The VESA organization that developed the DP standard mainly considers applications in the PC field, and the HDMI standard was developed by the Consumer Electronics Alliance. We can see HDMI on many consumer electronic devices, such as set-top boxes, TVs, projectors, computers, etc.
Therefore, professional level and enthusiast users will choose DP and affect the display of the main graphics card and display for more than 90% of the general users. So don’t worry too much about using DP or HDMI.
